In the manner that is customary in this field, the side member of this substructure has a rear portion, which extends horizontally in vehicle longitudinal direction along a stowage space of the vehicle, a first portion, which crosses under the passenger cell of the vehicle substantially linearly, and a second portion, which connects the two aforementioned portions to one another and runs obliquely to the vehicle longitudinal direction in a transition region between the rear axle of the vehicle and the passenger cell.
When the vehicle is involved in a collision and the side member has to absorb high forces in vehicle longitudinal direction, this oblique transition region is subjected to particularly high loads. In order to prevent the side member from initially giving way to the load in this transition region, a solution has been to more robustly construct this region than the portions of the side member before it and after it oriented in vehicle longitudinal direction. Such a structure which is variable across the side member can be readily realized by using deep-drawn upper and lower shells; since however the wall thickness of the shells is predetermined within narrow limits by the sheet metal used as source material during the deep-drawing, a higher load capacity of the side member in the transition region can substantially be achieved only through an enlarged cross section, through which room in the stowage space or in the passenger cell is lost.